JP2023110629A - Fixing device and image forming apparatus - Google Patents

Abstract

To provide a fixing device that can achieve both prevention of damage to a cam receiving member and a reduction in space and cost.SOLUTION: A fixing device comprises: a swingable plate-like pressure lever member 31 that presses one of a pair of rollers to the other; a cam member 41 that displaces the pressure lever member 31 between a position for maintaining the pressure contact state of the pair of rollers and a position for releasing the state; and a cam receiving member 32 that is disposed at a position of the pressure lever member 31 facing the cam member 41, and transmits a pressing force from the cam member 41 to the pressure lever member 31. When the thickness of the pressure lever member 31 is defined as t, the dimension of the cam receiving member 32 in the thickness direction of the pressure lever member 31, the dimension being the length of a surface in contact with the cam member 41 as W, and the dimension of the cam receiving member 32 in a direction orthogonal to the thickness direction of the pressure lever member 31, the dimension being the length from the contact position with the cam member 41 to one side face as L1, the relationship of L1≥0.6×(W-t)/2+0.2 is satisfied.SELECTED DRAWING: Figure 2

Description

The present invention relates to fixing devices and image forming apparatuses.

A fixing device installed in an image forming apparatus such as a copier, a printer, a facsimile machine, or the like includes a heating roller and a pressure roller. It is known to fix the above image by heat and pressure. Such a fixing device is provided with a contact/separation mechanism for moving the heat roller and the pressure roller closer to each other and away from each other.

The contact/separation mechanism generally includes a cam member that rotates to move the contact/separation members closer to each other (see, for example, Patent Document 1).
Patent Document 1 discloses a contact/separation mechanism for moving a contact/separation member closer to and away from the contact member by rotating the cam member, wherein the distance from the center of rotation of the cam member gradually increases over a region larger than half the circumference in the direction of rotation. An arrangement is disclosed that has a surface and is rotatable in one direction and the other.

In recent years, there has been a demand for space saving and cost reduction in image forming apparatuses.
In order to save space and reduce costs, it is conceivable to reduce the size and thickness of component parts. For example, as in the fixing device disclosed in Japanese Patent Application Laid-Open No. 2002-200300, space can be saved by using a flat pressure lever member that does not involve complicated processing. In addition, by using a resin material that can be easily processed for the cam member and the member that contacts the cam member, and by reducing the size of the parts, it is possible to reduce the amount of material used and reduce the cost.

However, restrictions on thinning and downsizing of constituent members may lead to a decrease in the strength of the members. In particular, there is a possibility that the cam receiving member, which receives pressure from the cam member, may be deformed by being subjected to repeated loads or damaged over time.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a fixing device that can achieve both prevention of damage to a cam receiving member and realization of space saving and cost reduction.

In order to solve the above-mentioned problems, the fixing device of the present invention includes a pair of rollers which are pressed against each other so as to be able to contact and separate from each other, nipping and conveying a recording medium, and one end of which is pivotally supported and the other end of which is engaged with an elastic member. a swingable plate-like pressure lever member for pressing one of the pair of rollers against the other; and a cam receiving member disposed at a position facing the cam member of the pressure lever member and transmitting a pressing force from the cam member to the pressure lever member, wherein the pressure is applied. The thickness of the lever member is t, the dimension of the cam receiving member in the thickness direction of the pressure lever member, the length of the surface that contacts the cam member is W, and the thickness direction of the pressure lever member is W. L1≧0.6×(W−t)/2+0.6×(W−t)/2+0.6×(W−t)/2+0.6×(W−t)/2+0.6×(W−t)/2+0.6×(W−t)/2+0. It is characterized by satisfying the relationship of 2.

According to the present invention, it is possible to provide a fixing device that can achieve both prevention of damage to the cam receiving member and realization of space saving and cost reduction.

1 is a schematic configuration diagram of a monochrome image forming apparatus according to an embodiment of the present invention; FIG. 1 is a schematic configuration diagram of a fixing device according to an exemplary embodiment; FIG. It is a figure which extracts and shows a cam member, a light-shielding member, and an optical sensor. 3 is a schematic configuration diagram of a drive system of a contact/separation mechanism according to the embodiment; FIG. 3 is a block diagram of the control system of the contact/separation mechanism according to the embodiment; FIG. FIG. 10 is a diagram for explaining the separation operation of the pressure roller by the cam member; FIG. 10 is a diagram for explaining an approaching operation of the pressure roller by a cam member; FIG. 5 is a cam diagram showing the relationship between the rotation angle and radius of the cam member; FIG. 4 is a perspective view showing an example of a cam receiving member arranged on a pressing lever member; FIG. 5 is an explanatory diagram showing a state in which a cam member and a cam receiving member are in contact with each other; FIG. 4 is an explanatory diagram of load and stress applied to a cam receiving member; FIG. 5 is an explanatory diagram of the dimensions of the cam receiving member in the thickness direction of the pressing lever member; 4A is a graph showing the position of the cam receiving member where the load is received, and FIG. 4B is a graph showing the stress distribution of the cam receiving member. 4 is a graph showing changes in stress value when the load position of the cam receiving member is changed. 4 is a graph showing results of stress analysis simulation for combinations of values of Δt and L1; FIG. 4 is an explanatory diagram showing an example of a cam receiving member; 7 is a graph showing the results of stress analysis simulation for the R shape of the cam receiving member; FIG. 10 is an explanatory diagram showing an unstable contact state between the pressurizing lever member and the cam receiving member; FIG. 4 is an explanatory diagram showing an example of an engagement structure between a cam receiving member and a pressurizing lever member; FIG. 4 is a perspective view showing an example of an engagement structure between a cam receiving member and a pressing lever member; FIG. 5 is a perspective view showing an example of fitting between a pressurizing lever member having a wall portion and a cam receiving member; FIG. 5 is an explanatory view showing an example of fitting between a pressure lever member having a wall portion and a cam receiving member; FIG. 10 is a diagram for explaining inclination of posture due to a gap between a pressurizing lever member and a cam receiving member; FIG. 10 is a perspective view showing an example of a cam receiving member fitted to a pressure lever member having a wall; FIG. 4 is an explanatory diagram of dimensions of a cam receiving member fitted to a pressurizing lever member having a wall; 4 is a graph showing results of stress analysis simulation for combinations of values of Δt and L2; FIG. 4 is a perspective view showing an example of a cam receiving member arranged on a pressing lever member; FIG. 5 is an explanatory diagram showing the R shape and stress of the bottom surface of the concave portion of the cam receiving member; FIG. 4 is a perspective view showing an example of a shape of a contact surface of a cam receiving member with a cam member; FIG. 4 is a cross-sectional view showing an example of the shape of a contact surface of a cam receiving member with a cam member; 1 is a schematic configuration diagram of a fixing device having a fixing belt; FIG. 1 is a schematic configuration diagram of a fixing device in which a fixing roller approaches and separates from an opposing roller; FIG.

A fixing device and an image forming apparatus according to the present invention will be described below with reference to the drawings. In addition, the present invention is not limited to the embodiments shown below, and can be changed within the scope of those skilled in the art, such as other embodiments, additions, modifications, deletions, etc. is also included in the scope of the present invention as long as the functions and effects of the present invention are exhibited.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to one embodiment of the present invention.
The configuration of the fixing device according to the present invention can be applied to both electrophotographic image forming apparatuses and ink jet image forming apparatuses. An example of a fixing device installed in an electrophotographic image forming apparatus will be described below. In an inkjet image forming apparatus, for example, the fixing device is applied as means for drying ink by heating a recording medium with a heating roller. be able to.

Further, in the following embodiments, the "recording medium" is explained as "paper", but the "recording medium" is not limited to paper (paper). The "recording medium" includes not only paper but also OHP sheets, fabrics, metal sheets, plastic films, or prepreg sheets in which carbon fibers are previously impregnated with resin. The term "recording medium" also includes media to which developer and ink can be applied, recording paper, and recording sheets. In addition to plain paper, "paper" includes thick paper, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and the like.

In addition, the term "image formation" used in the following description refers not only to imparting meaningful images, such as characters and figures, to a medium, but also to imparting meaningless images, such as patterns, to a medium. also means

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to one embodiment of the present invention.
First, referring to FIG. 1, the overall configuration and operation of the image forming apparatus will be described. In addition to printers, image forming apparatuses to which the present invention is applied include copiers, facsimiles alone, and multifunction machines having at least two functions of copiers, printers, facsimiles, and scanners.

The image forming apparatus shown in FIG. 1 is a monochrome image forming apparatus. A process unit 1 as an image forming unit is detachably attached to the apparatus main body (image forming apparatus main body) 100 . The process unit 1 includes a photoreceptor 2 as an image carrier that carries an image on its surface, a charging roller 3 as a charging means for charging the surface of the photoreceptor 2, and a latent image on the photoreceptor 2 to form a visible image. A developing device 4 as developing means and a cleaning blade 5 as cleaning means for cleaning the surface of the photoreceptor 2 are provided. Also, an LED head array 6 as exposure means for exposing the surface of the photoreceptor 2 is arranged at a position facing the photoreceptor 2 .

To the process unit 1, a toner cartridge 7 as a powder container for containing toner, which is powder for image formation, is detachably mounted. The toner cartridge 7 has an unused toner storage section 8 that stores unused toner and a waste toner storage section 9 that stores used waste toner.

The image forming apparatus also includes a transfer device 10 for transferring an image onto a sheet of paper as a recording medium, a paper feeding device 11 for supplying the paper, a fixing device 12 for fixing the image transferred onto the paper, and an external device for fixing the image transferred to the paper. and a pair of registration rollers 17 as timing rollers.

The transfer device 10 includes a transfer roller 14 as a transfer member. The transfer roller 14 is arranged so as to come into contact with the photoreceptor 2 when the process unit 1 is attached to the apparatus main body 100 . Further, the transfer roller 14 is connected to a power supply (not shown), and is applied with a predetermined direct current (DC) and/or alternating current (AC) voltage.

The paper feeder 11 includes a paper feed cassette 15 containing paper P as a recording medium, and a paper feed roller 16 for feeding the paper P contained in the paper feed cassette 15 . In addition to plain paper, paper P includes thick paper, thin paper, postcards, envelopes, coated paper (coated paper, art paper, etc.), tracing paper, and the like. Furthermore, it is also possible to use an OHP sheet, an OHP film, or the like as a recording medium other than paper.

The fixing device 12 includes a pair of rotating bodies facing each other. One rotating body is a fixing roller 18 as a fixing rotating body for fixing an image on paper, and the other rotating body is a pressing roller 19 as a pressure rotating body that presses against the fixing roller 18 . be. The fixing roller 18 is internally provided with heating means (for example, a halogen heater) 22 . The fixing roller 18 and pressure roller 19 are in contact with each other, and a fixing nip is formed between both rollers 18 and 19 .

The paper discharge device 13 includes a pair of paper discharge rollers 20 for discharging the paper outside the device. Further, on the upper surface of the exterior of the apparatus main body 100, a paper discharge tray 21 for placing paper discharged by the paper discharge rollers 20 is formed.

Further, in the apparatus main body 100, from the paper feed cassette 15, through the registration roller 17, the image transfer portion (transfer nip) between the transfer roller 14 and the photoreceptor 2, the fixing device 12, the paper discharge roller 20 A transport path 101 is provided for transporting the paper P to the . Further, in the image forming apparatus 100, a double-sided transport path 102 is provided for transporting the paper P that has passed through the fixing device 12 to the image transfer section again when double-sided printing is performed.

Next, the image forming operation of the image forming apparatus according to this embodiment will be described with reference to FIG.
When the image forming operation is started, the photoreceptor 2 is driven to rotate, and the charging roller 3 uniformly charges the surface of the photoreceptor 2 to a predetermined polarity. Next, the LED head array 6 exposes the charged surface of the photoreceptor 2 based on image information from a reading device, computer, or the like to form an electrostatic latent image. Then, toner is supplied to the electrostatic latent image on the photosensitive member 2 by the developing device 4, so that the electrostatic latent image is developed (visualized) as a toner image.

Further, when the image forming operation is started, the paper feed roller 16 starts rotating, and the paper P is sent out from the paper feed cassette 15 . The conveying of the sent paper P is temporarily stopped by the registration rollers 17 . After that, the registration rollers 17 are started to rotate at a predetermined timing, and the sheet P is conveyed to the image transfer section in synchronization with the timing when the toner image on the photoreceptor 2 reaches the image transfer section.

Then, when the paper P is conveyed to the image transfer section, the toner image on the photoreceptor 2 is transferred onto the paper P by a transfer electric field generated by applying a predetermined voltage to the transfer roller 14 . Further, the toner on the photoreceptor 2 that has not been transferred to the paper P at this time is removed by the cleaning blade 5 and collected in the waste toner container 9 of the toner cartridge 7 .

The paper P onto which the toner image has been transferred is conveyed to the fixing device 12, passes through a fixing nip formed by the fixing roller 18 and the pressure roller 19, and is heated and pressurized to fix the toner on the paper P. The image is fixed. Then, the paper P is discharged outside the apparatus by the paper discharge rollers 20 and placed on the paper discharge tray 21 .

In the case of double-sided printing, the paper P that has passed through the fixing device 12 is switched back and sent to the double-sided conveying path 102 without being discharged outside the device. The paper P passes through the double-sided conveying path 102 and is sent to the conveying path 101 on the front side of the registration rollers 17 , and is again conveyed to the image transfer section by the registration rollers 17 . Then, the image is transferred to the back surface of the paper P, and after the image on the back surface side is fixed by the fixing device 12, the paper P is discharged outside the apparatus.

FIG. 2 is a schematic configuration diagram of the fixing device according to this embodiment.
Hereinafter, the fixing device 12 to which the present invention is applied will be described in detail with reference to FIG.
Both ends of the fixing roller 18 and the pressure roller 19 are rotatably supported by a pair of support members 25 via bearings 23 and 24, respectively. When a driving force is transmitted to the fixing roller 18 from a driving source provided in the main body of the apparatus, the fixing roller 18 rotates in the direction indicated by the arrow A in FIG. 2 is driven to rotate in the direction indicated by the arrow B1. Contrary to this embodiment, the pressure roller 19 may be the drive roller and the fixing roller 18 may be the driven roller.

When the sheet enters the fixing nip 80 from the direction indicated by the arrow C1 in FIG. The paper is conveyed while being nipped by the rollers 19 . At this time, the unfixed image on the paper is heated by the heat of the fixing roller 18 and pressed by the fixing roller 18 and the pressure roller 19 to fix the image on the paper. Then, the sheet on which the image is fixed is discharged from the fixing nip 80 in the direction of arrow C2 in FIG.

Further, the pressure roller 19 is supported by the support member 25 so as to be able to approach and separate from the fixing roller 18 in the arrow B2 direction in FIG. Specifically, the bearing 24 that supports the pressure roller 19 is fitted in a bearing guide portion 25b, which is a rectangular hole provided in the support member 25, and the bearing 24 moves along the bearing guide portion 25b. By being guided, the pressure roller 19 approaches and separates from the fixing roller 18 . On the other hand, the bearings 23 that support the fixing rollers 18 are fitted in bearing fitting portions 25a, which are circular holes provided in each supporting member 25, and the fixing rollers 18 are positioned so that their shafts are positioned perpendicular to the axial direction. fixed to prevent it from moving.

The fixing device 12 according to the present embodiment also includes a pressure lever member 31 that presses the pressure roller 19 against the fixing roller 18, and a biasing member that biases the pressure lever member 31 in the pressure direction. A pressure spring 36 is provided. One pressure lever member 31 and one elastic member (hereinafter also referred to as “pressure spring”) 36 are provided at both ends of the pressure roller 19 . One end 31d of the pressure lever member 31 is attached to a support shaft 33 provided at the bottom of the support member 25, and is configured to be rotatable around the support shaft 33 in the direction of arrow α in FIG. Each pressurizing spring 36 is attached by hooking onto hooking portions 31c and 25c provided on the other end portion 31b side of the pressurizing lever member 31 and the upper portion of the support member 25 . As a result, the other end 31b of the pressing lever member 31 is held in a state of being constantly pulled upward in the drawing by the pressing spring .
The pressure lever member 31 presses the bearing 24 supporting the pressure roller 19 via the pad 34 fitted in the bearing guide portion 25 b of the support member 25 , thereby moving the pressure roller 19 toward the fixing roller 18 . pressurized.

The fixing device 12 according to the present embodiment also includes a cam member 41 as a contact/separation mechanism for moving the pressure roller 19 toward and away from the fixing roller 18 .
The cam members 41 are provided on both end sides of a rotary shaft 42 rotatably supported by a pair of support members 25 . When the rotating shaft 42 rotates, the pair of cam members 41 rotate together with the rotating shaft 42 . The cam member 41 also has a cam surface 41a whose distance from the center of rotation changes in the direction of rotation. By pulling the pressure lever member 31 by the pressure spring 36, the cam receiving member 32 provided on the pressure lever member 31 is held in contact with the cam surface 41a. In this state, when the cam member 41 rotates in one direction, the pressure lever member 31 is pushed downward in the figure by the cam surface 41a, so that the pressure roller 19 is separated from the fixing roller 18, and the cam member 41 rotates in the reverse direction, the pressure lever member 31 is returned upward in the figure, so that the pressure roller 19 approaches the fixing roller 18 . A detailed contacting/separating operation by the cam member 41 will be described later.

The fixing device 12 according to the present embodiment also includes an optical sensor 51 and a light blocking member 52 as rotational position detecting means for detecting the rotational position (rotational angle) of the cam member 41 . The optical sensor 51 is a transmissive optical sensor, and has a light projecting portion that emits light and a light receiving portion that receives the light emitted from the light projecting portion. The light shielding member 52 is a member to be detected that shields or transmits the irradiation light of the optical sensor 51 by rotating integrally with the cam member 41 and whose rotational position is detected by the optical sensor 51 by switching the presence/absence of light reception. be. The optical sensor 51 and the light blocking member 52 are provided only on one cam member 41 side of the two cam members 41 .

FIG. 3 is a diagram showing the cam member, the light shielding member, and the optical sensor extracted.
As shown in FIG. 3, the cam surface 41a provided on the cam member 41 is formed such that the distance from the rotation center gradually increases clockwise in the drawing. The cam surface 41a is provided over a region larger than half the circumference (180°) in the rotational direction. Specifically, in the present embodiment, from the lowest point e1 at which the distance from the center of rotation of the cam surface 41a is the shortest to the highest point e2 at which the distance from the center of rotation of the cam surface 41a is the greatest is about 270°. placed across.

The light-shielding member 52 includes a long light-shielding portion 52a as a detection area that is long in the rotational direction (the length in the rotational direction is J1) and a shorter light-shielding portion 52a in the rotational direction (the length in the rotational direction is J2). ) and a short light-shielding portion 52b as a detection area. Both the long light shielding portion 52a and the short light shielding portion 52b shield the irradiation light by passing through the light irradiation portion H of the optical sensor 51 as they rotate. A hole (light-transmitting portion) 52j through which the light emitted from the optical sensor 51 is transmitted is formed between the long light-shielding portion 52a and the short light-shielding portion 52b.

FIG. 4 is a schematic configuration diagram of the drive system of the contact/separation mechanism according to this embodiment.
As shown in FIG. 4 , the driving system includes a motor 43 as a driving source and a gear train 44 that transmits the driving force from the motor 43 to the cam member 41 and the light blocking member 52 . In this embodiment, a compact and inexpensive DC brush motor is used as the motor 43 . The gear train 44 includes a first worm gear 45 attached to the output shaft of the motor 43 , a second worm gear 46 meshing with the first worm gear 45 , and a first flat gear 46 integrally provided with the second worm gear 46 . It is composed of a gear 47 and a second spur gear 48 that meshes with the first spur gear 47 and is provided integrally with the light shielding member 52 . When the output shaft of the motor 43 rotates in one direction or the opposite direction, the worm gears 45 and 46 and the spur gears 47 and 48 rotate, and the second spur gear 48 and the light blocking member 52 rotate together. Then, each cam member 41 rotates in one direction (the direction indicated by arrow F in FIG. 3) or in the opposite direction (the direction indicated by arrow G in FIG. 3) via the rotating shaft 42. As shown in FIG.

FIG. 5 is a block diagram of the control system of the contact/separation mechanism according to this embodiment.
As shown in FIG. 5, the control system includes a control unit 60 that controls the rotation of the cam member 41, the optical sensor 51 that detects the rotational position of the cam member 41, and the rotation time of the cam member 41. A timer 70 is provided.
The control unit 60 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. provided in the image forming apparatus main body. The control unit 60 controls the rotation of the cam member 41 by controlling the drive of the motor 43 based on the signal detected by the optical sensor 51 and the time measured by the timer 70 . The control unit 60 is also set to control the timing of starting and stopping time measurement by the timer 70 based on the signal detected by the optical sensor 51 .

In the fixing device according to the present embodiment, the pressure roller 19 can be moved toward or away from the fixing roller 18 so that the pressure applied to the fixing nip 80 can be changed.
6 and 7, the contact/separation operation of the pressure roller 19 by the cam member 41 (the pressure release operation when the pressure is released from the normal pressure and the pressure operation when the pressure is returned to the normal pressure) will be described below. do.

FIG. 6A shows a state in which the cam receiving member 32 provided on the pressing lever member 31 is in contact with the cam surface 41a on the side of the lowest point e1. In this state, the pressure roller 19 shown in FIG. 2 approaches the fixing roller 18 and is pressed with normal pressure.

When the cam member 41 is rotated counterclockwise in the drawing from the state shown in FIG. 6A to the state shown in FIG. 6B, the cam surface 41a slides against the cam receiving member 32 to The contact position of the cam receiving member 32 with respect to the surface 41a relatively moves from the lowest point e1 side to the highest point e2 side. Accordingly, the cam receiving member 32 is pushed downward in the figure by the cam surface 41 a , and the pressure lever member 31 retreats from the bearing of the pressure roller 19 , thereby causing the pressure roller 19 to move against the fixing roller 18 . and move away from each other.

Then, as shown in FIG. 6C, when the contact position of the cam receiving member 32 with the cam surface 41a reaches the uppermost point e2, the separation operation of the pressure roller 19 from the fixing roller 18 is completed, and the fixing nip is completed. A depressurized state is created in which the applied pressure is smaller than the normal applied pressure. At this point, the rotation of the cam member 41 is stopped.

On the other hand, when the cam member 41 is rotated clockwise (in the direction opposite to the direction of rotation during transition to pressure release) as shown in FIG. 7B from the pressure release state shown in FIG. 7A, , the cam surface 41a slides against the cam receiving member 32, and the contact position of the cam receiving member 32 with respect to the cam surface 41a relatively moves from the highest point e2 to the lowest point e1. Along with this, the cam receiving member 32 is pulled upward in the figure by the biasing force of the pressure spring 36, and the pressure lever member 31 presses the bearing of the pressure roller, thereby causing the pressure roller 19 to move toward the fixing roller 18. move toward the

Then, as shown in FIG. 7C, when the contact position of the cam receiving member 32 with respect to the cam surface 41a reaches the lowest point e1, the pressure roller 19 approaches the fixing roller 18, and the fixing nip is formed. The pressurization force at 80 is increased back to normal pressurization. At this point, the rotation of the cam member 41 is stopped.

As described above, in the fixing device according to the present embodiment, the cam member 41 is rotated in one direction when the pressure roller 19 and the fixing roller 18 are separated from each other, and when the pressure roller 19 is brought closer to the fixing roller 18, the cam member 41 rotates in one direction. By rotating the cam member 41 in the opposite direction, the same cam surface 41a is used to push and move the pressure lever member 31 and return it.

FIG. 8 is a cam diagram showing the relationship between the rotation angle and radius of the cam member 41. As shown in FIG.
In order to allow the cam member 41 to operate smoothly, the cam surface 41a is generally formed into a sinusoidal curve as shown in FIG. In this way, by reducing the amount of change in the cam surface 41a as the load applied to the cam surface 41a increases, sudden load changes are prevented, the operation is stabilized, the load on the drive motor is reduced, and abnormal noise is generated. can be prevented.
The cam surface 41a has a large curvature when the load is small, and a small curvature when the load is large. Therefore, in the cam diagram of FIG. I know you are.

The cam receiving member 32 provided in the fixing device according to the present invention has a reduced size and shape while satisfying the required strength based on the contact portion with the cam member 41 and the contact portion with the pressure lever member 31. Designed. This makes it possible to optimize the size and arrangement of the members, and by selecting appropriate materials, it is possible to save space, reduce costs, and improve durability. Hereinafter, the configuration related to the design of the cam receiving member 32 of the fixing device according to the present invention will be described.

The fixing device according to the present invention includes a pair of rollers (for example, a pressure roller 19 and a fixing roller 18 shown in FIG. 2) which are in pressure contact with each other so as to be freely contactable and separate and convey a recording medium between them (for example, a pressure roller 19 and a fixing roller 18 shown in FIG. 2). An elastic member (pressure spring) 36 is locked at the other end, and a plate-like pressure lever member 31 that can swing to press one of the pair of rollers against the other, and a position where the pair of rollers are held in pressure contact. and a cam member 41 for displacing the pressure lever member 31 between the release position and the position where the pressure lever member 31 is opposed to the cam member 41. The pressure force from the cam member 41 is applied to the pressure lever member and a cam receiving member 32 that transmits power to the pressure lever member 31, where t is the thickness of the pressure lever member 31, the dimension of the cam receiving member 32 in the thickness direction of the pressure lever member 31, and the surface that contacts the cam member 41. Let W be the length, and L1 be the dimension of the cam receiving member 32 in the direction orthogonal to the thickness direction of the pressure lever member 31 from the contact position with the cam member 41 to one side surface. When, the relationship of the following formula (1) is satisfied.
L1≧0.6×(W−t)/2+0.2 Expression (1)

The symbols in formula (1) will be described below with reference to FIGS. 10, 11 and 12. FIG.
FIG. 10 is an explanatory diagram showing a state in which the cam member 41 and the cam receiving member 32 are in contact with each other, and FIG.
As shown in FIG. 10, the cam receiving member 32 receives a load M at a contact position 32b with the cam member 41 from the upper side of the drawing, and a contact surface receiving surface with the pressing lever member 31 from the lower side of the drawing. is receiving a load N.
In FIG. 10, the installation surface of the cam receiving member 32 and the contact surface with the pressure lever member 31 are shown inclined based on the installation mode of the fixing device 12 shown in FIG. Now, we will explain these with a diagram showing them horizontally.

As shown in FIG. 11, "D" is the overall length of the cam receiving member 32 in the direction perpendicular to the thickness direction of the pressing lever member 31 (x direction in the drawing).
"L1" is the dimension of the cam receiving member 32 in the direction perpendicular to the thickness direction of the pressing lever member 31 (the X direction in the drawing), and is measured from the contact position 32a with the cam member 41 to one side surface ( It is the length to the left side surface 32c).
When the contact portion between the cam receiving member 32 and the cam member 41 has a width in the direction perpendicular to the thickness direction of the pressing lever member 31 (the X direction in the drawing), the contact position 32a The center in the X direction of the region in contact with is used as a reference.

FIG. 12 is an explanatory diagram of the dimensions of the cam receiving member 32 in the thickness direction of the pressing lever member 31. As shown in FIG.
As shown in FIG. 12, "W" is the entire length of the surface (abutting area) of the cam receiving member 32 that contacts the cam member 41 in the thickness direction (the Y direction in the drawing) of the pressure lever member 31. .
Since the area of contact with the cam member 41 differs depending on the shape of the surface of the cam receiving member 32 facing the cam member 41, the value of "W" does not necessarily match the total length of the cam receiving member in the Y direction.
“t” is the thickness of the pressing lever member 31 . The thickness of the pressing lever member 31 refers to the plate thickness of the plate-shaped sheet metal member forming the pressing lever member 31 .
“Δt” is a variable represented by “(W−t)/2” in formula (1), and the area (length W) that contacts the cam member 41 contacts the pressurizing lever member 31 . It is the length of one side in the Y direction corresponding to the outer portion of the contacting region 32f.

"Sc" in FIG. 11 is the load stress value generated at the contact position 32a of the cam receiving member 32 with the cam member 41, and is a value calculated by simulation.
"St" is the load stress value generated at the upper corner portion of the left end surface 32c of the cam receiving member 32, that is, the portion where cracks are likely to occur and the starting point of member damage, and is a value calculated by simulation. is.
A graph relating to these simulations is shown in FIG.

FIG. 13(A) is a diagram for explaining the positions (M1, M2, M3) of the cam receiving member 32 subjected to the simulation, and FIG. 13(B) is a graph showing the stress distribution corresponding to each position. be.
As shown in FIG. 13(A), the contact position 32a with the cam member 41 is M1 when the center portion of the X direction left and right (length D) is the load, and the vicinity of one side end (left side 32c) is M3 indicates the load when the load is set to 100 degrees, and M2 indicates the load when the load is set at an intermediate position. Note that the loads of M1, M2 and M3 are all equal. These stress distributions in the X direction (length D) are shown in FIG. 13(B).

As can be seen from the graph of FIG. 13(B), in any case, the stress value "Sc" at the contact position 32a with the cam member 41 is the highest. Moreover, although the loads of M1, M2, and M3 are the same, the stress increases (M1 is the largest) in order of contact position 32a closer to the end side in the X direction.
The stress value "St" is the leftmost value in the graph (the value at the upper corner of the left side surface 32c). It can be seen that the stress is increased (M1 is maximum).

FIG. 14 is a graph showing changes in stress values when the contact position 32a (the position of the load M) of the cam receiving member 32 with the cam member 41 is changed from the left end to the right end in the X direction. Note that the load value is constant.
The horizontal axis L is the length from the contact position 32a of the cam receiving member 32 with the cam member 41 to the left end (left side surface 32c), and the contact position 32a is on the left end (left side surface 32c) side. The value of L increases as the contact position 32a moves toward the right end (right side surface 32d) of the contact position 32a.
As can be seen from the graph of FIG. 14, the values of Sc and St are maximum near L=0, and the values of Sc and St are close to each other. The value of Sc decreases as the value of L increases, and becomes constant at the value enclosed by the dashed circle after Lx. The value of St also decreases as the value of L increases, and even after Lx, it becomes even smaller than the value enclosed by the dashed circle. That is, at positions after Lx, the divergence between the values of Sc and St increases.

As a result of examining the crack occurrence situation in the actual cam receiving member 32, early crack occurrence was observed in the range of L from 0 to Lx. This is because a high stress is maintained in the region from the contact position 32a of the cam receiving member 32 with the cam member 41 to the upper end corner of the left end surface 32c, and creep fatigue tends to progress. Conceivable.
Therefore, by providing the contact position 32a of the cam member 41 at a position where L is larger than the range of L (0 to Lx) where the values of Sc and St are approximate values, the occurrence of cracks is prevented and the member It is considered possible to prevent the creep fracture of

On the other hand, it is the value of "Δt" shown in FIG. 12 that contributes to the condition (threshold value) for dividing the case where the value of Sc and the value of St diverge from each other in correspondence with L and the case where they do not diverge. “Δt” is a variable represented by “(W−t)/2” in formula (1).
FIG. 15 shows the results of stress analysis simulation for combinations of Δt and L values.

In the graph of FIG. 15, the horizontal axis is Δt (=(W−t)/2) and the vertical axis is L, the value of L at which the value of Sc and the value of St begin to diverge (for example, Lx in FIG. 14) The result of plotting is indicated by "●". When the straight line obtained from "●" is represented by an approximation formula, the following formula (2) is obtained.
L=0.6×Δt+0.2 Expression (2)

In the design of the cam receiving member 32, if the value of Δt is determined from the thickness t of the pressurizing lever member 31 made of a flat sheet metal member, the contact position 32a with the cam member 41 is set to one side of the cam receiving member 32. (one side surface in the direction perpendicular to the thickness direction of the pressure lever member) is set to a position larger than L obtained by the formula (2), cracks can be prevented from occurring.
That is, in the fixing device of the present embodiment, when the length from the contact position 32a with the cam member 41 to one side is L1, L1≧0.6×(W−t)/2+0.2. Thereby, the occurrence of cracks can be prevented.

As shown in equation (2), since the variable Δt determines the deviation between the value of Sc and the value of St, the optimal shape can be determined. After determining the optimum shape, the material of the cam receiving member 32 and the magnitude of the stress received from the cam member 41 should be considered. is eliminated, and an increase in cost can be prevented.

As shown in the graph of FIG. 14, the value of St decreases as the value of L increases, and becomes almost 0 near the maximum value of L. When the value of St is close to 0, the possibility of cracks occurring in the cam receiving member 32 is extremely low, so there is no need to increase the value of L any further in the design.
FIG. 15 shows the result of stress analysis simulation for combinations of L values when the value of St is 0. In FIG.

In the graph of FIG. 15, with Δt (=(W−t)/2) on the horizontal axis and L on the vertical axis, the result of plotting the value of L when the value of St is 0 is indicated by "▴". When the straight line obtained from "▴" is represented by an approximation formula, the following formula (3) is obtained.
L=1.3×Δt+1.25 Expression (3)

In FIG. 15, the range La surrounded by the straight line of formula (2) and the straight line of formula (3) is the proper range of Δt.

In the design of the cam receiving member 32, if the value of Δt is determined from the thickness t of the pressurizing lever member 31 made of a flat sheet metal member, the contact position 32a with the cam member 41 is set to one side of the cam receiving member 32. (one side surface in the direction orthogonal to the thickness direction of the pressure lever member) at a position smaller than L calculated by formula (3) and a position larger than L calculated by formula (2). By doing so, it is possible to prevent the occurrence of cracks and reduce the size of the member.
That is, in the fixing device of the present embodiment, when the length from the contact position 32a with the cam member 41 to one side surface is L1, further L1≦1.3×(W−t)/2+1.25. By satisfying the relationship, it is possible to both prevent the occurrence of cracks and reduce the size of the member.

In FIG. 15, the range La surrounded by the straight line of formula (2) and the straight line of formula (3) is the proper range of Δt.

In formula (3), the variable .DELTA.t can be taken into consideration in the same manner as in formula (2), and the optimum shape can be determined by focusing only on the relationship between the contact position 32a between the cam receiving member 32 and the cam member 41. can. After determining the optimum shape, the material of the cam receiving member 32 and the magnitude of the stress received from the cam member 41 should be considered. is eliminated, and an increase in cost can be prevented.
When further narrowing down the optimum range of the value of L, the strength of the material of the cam receiving member 32 and the magnitude of the stress received from the cam member 41 can be considered.

In this way, by considering the relationship between L and Δt, it is possible to prevent the cam receiving member 32 from being designed larger than necessary. The size and arrangement of parts can be optimized, and as a result, space saving and cost reduction can be achieved. Furthermore, by preventing breakage of the member, the durability of the fixing device can be improved.

Next, an example of the outer shape of the cam receiving member 32 will be described.
(First embodiment)
An example of this embodiment is shown in FIG.
FIG. 16 is a side view showing an example of the outer shape of the cam receiving member 32. As shown in FIG.
At least one of the corners (32h, 32g) formed by the surface facing the cam member 41 and the left and right outer surfaces in the thickness direction of the pressure lever member 31 of the cam receiving member 32 is rounded. is preferred.
As shown in FIG. 16, the R-shaped corner is preferably an upper corner 32h of the left end face 32c, that is, a corner that is likely to cause cracks and is a starting point of member breakage.

FIG. 17 is a graph showing the results of a stress analysis simulation performed on changes in the load stress St when the size of the R shape of the corner portion 32h shown in FIG. 16 is changed.
The magnitude of the load M from the cam member 41 and the position of the load (contact position 32a with the cam member 41) are constant.
As shown in FIG. 17, it can be seen that the stress generated in the corner 32h is smaller in the range of R0.5 to R2 than in the case of non-R shape. By rounding the corners in this manner, the load stress St at the locations where cracks are likely to occur can be reduced.

(Second embodiment)
The features of this embodiment are shown in FIGS. 9 and 12. FIG.
FIG. 9 is a perspective view showing an example of the cam receiving member 32 arranged on the pressing lever member 31. As shown in FIG. 12 shows a cross-sectional view of the cam receiving member 32 of FIG. 9 in the thickness direction of the pressurizing lever member 31. As shown in FIG.
As shown in FIGS. 9 and 12, the cam receiving member 32 is a member having a substantially U-shaped cross section, and includes a pressed surface 41a which receives the pressing force from the cam member 41 of the pressing lever member 31, and a pressing surface 41a. It is preferable to have a shape that fits so as to cover at least a part of both side surfaces in the thickness direction of the member 31 . Further, it is preferable that the difference between the width of the concave portion of the cam receiving member 32 and the thickness of the pressurizing lever member 31 is small.

FIG. 18 is an explanatory diagram showing an example of an unstable contact state between the pressing lever member 31 and the cam receiving member 32. FIG.
The cam receiving member 32 may have a shape that does not cover both side surfaces in the thickness direction of the pressing lever member 31 as shown in FIG. , the contact with the pressure lever member 31 may become unstable if the gap with the pressure lever member 31 is large. As a result of partial contact, a local load is applied to the contact portion indicated by 32j in the drawing, and damage may occur starting from that portion.

By forming the cam receiving member 32 into a shape as shown in FIGS. 9 and 12, there is no rattling when it is engaged with the pressing lever member 31, and the mounting state is stable, so that an abnormal stress load is generated. It is possible to prevent problems such as early breakage from occurring.
In addition, it is possible to prevent troubles such as falling off not only when using the device but also when assembling parts.

(Third Embodiment)
An example of this embodiment is shown in FIGS. 19 and 20. FIG.
19 and 20 are explanatory diagrams showing an example of the engagement structure 35 between the cam receiving member 32 and the pressing lever member 31. FIG. 19 is a cross-sectional view of the pressure lever member 31 in the thickness direction, and FIG. 20 is a perspective view of the embodiment of FIG. 19(B).
The cam receiving member 32 and the pressing lever member 31 preferably have an engaging structure 35 that engages with each other. The engagement structure 35 functions, for example, as a fall prevention mechanism.

FIG. 19 shows a state where the cam receiving member 32 and the pressing lever member 31 are fitted in the upper stage, and a state before the cam receiving member 32 and the pressing lever member 31 are fitted in the lower stage.
FIGS. 19A and 19B show an example in which the pressure lever member 31 has an engagement recess 35b and engages with the engagement projection 35a of the cam receiving member 32. FIG.
19(C) and 19(D) show an example in which the engaging convex portion 35a of the cam receiving member 32 engages with the bottom portion of the pressing lever member 31. FIG.

The shape of the engagement concave portion 35b provided in the pressure lever member 31 is not particularly limited as long as it engages with the engagement convex portion 35a of the cam receiving member 32, and penetrates the pressure lever member 31 in the thickness direction. It may be an opening or a groove-like structure.
Further, the shape of the engaging convex portion 35a provided on the cam receiving member 32 is not particularly limited, and may be a projecting shape as shown in FIGS. 19(A) and 19(C). B) and claw-shaped ones having a triangular cross section as shown in FIG. 19(C).
Regardless of the shape, it is preferable that the strength of the member is not lowered and complicated processing is not required.

By having a structure in which the cam receiving member 32 and the pressure lever member 31 are engaged with each other as in the present embodiment, a stable mounting state can be achieved as in the above-described second embodiment, so that an abnormal stress load is generated. It is possible to prevent troubles such as early breakage from occurring, and to prevent troubles such as falling off not only during use of the device but also during assembly of parts.

(Fourth embodiment)
An example of this embodiment is shown in FIGS. 21 to 25. FIG.
As shown in FIG. 21, the pressurizing lever member 31 may have a shape having a wall portion 31k that protrudes in the vertical direction with respect to the pressed surface 31a that receives the pressing force from the cam member 41. As shown in FIG. Further, the cam receiving member 32 may be shaped to fit into the wall portion 31k (wall portion fitting portion 32k). As in the second embodiment, the cam receiving member 32 preferably has a shape that is fitted so as to cover at least a part of both side surfaces of the pressing lever member 31 in the thickness direction.

The cam receiving member 32 fits into the pressed surface 31a in the thickness direction of the pressure lever member 31, and fits into the wall portion 31k in the direction perpendicular to the thickness direction of the pressure lever member 31. Therefore, the mounting state is improved. It is stable, prevents the occurrence of abnormal stress loads, and prevents the occurrence of defects such as premature breakage.

22(A) is a cross-sectional view in the X direction of FIG. 21, and FIG. 22(B) is a cross-sectional view showing a state in which the cam receiving member 32 is attached to the pressurizing lever member 31. FIG. FIG. 22C is a cross-sectional view of an example of the second embodiment shown for comparison.
As shown in FIG. 22(B), the wall portion fitting portion 32k of the cam receiving member 32 and the wall portion 31k of the pressing lever member 31 are overlapped by a length K2 longer than K1 in the vertical direction of the figure. ing.

FIG. 23 is a cross-sectional view in the Y direction of FIGS. 21 and 22(B), and is a diagram for explaining the inclination of the posture due to the gap u between the pressing lever member 31 and the cam receiving member 32. FIG. 23(A) and 23(B) are cross-sectional views seen from the left side of FIG. 22(B), and FIGS. 23(C) and 23(D) are cross-sectional views seen from the right side of FIG. 22(B). It is a diagram.
It is preferable that the gap u generated when the pressing lever member 31 and the cam receiving member 32 are fitted together is small. If there is no gap at all, normal operation may not be possible, so it is preferable to provide a certain amount of gap u in the fitted state in consideration of dimensional variations between parts.

On the other hand, if the gap u is large, tilting occurs as shown in FIGS. The amount of this inclination is determined by the length of overlap between the cam receiving member 32 and the pressurizing lever member 31 indicated by K1 and K2 in the vertical direction of FIGS. 23(A) and 23(C).
The inclination is reduced by changing the overlap length from K1 to K2, and as a result, the local stress indicated by the arrow in the figure is also reduced.

FIG. 24 is a perspective view of the cam receiving member 32 of this embodiment, and FIG. 24(B) is a view seen from the rear (wall portion 31k side) in FIG. 24(A).
25A is an X-direction cross-sectional view of the cam receiving member 32 in this embodiment, and FIG. 25B is a plan view of the surface of the cam receiving member 32 facing the cam member 41 in this embodiment.
In this embodiment, the shape of the surface of the cam receiving member 32 that receives the load from the cam member 41 has a concave portion whose horizontal cross section is substantially U-shaped due to the extended wall fitting portion 32k. Corners 32m are provided on both sides of the bottom surface of the recess. In the drawing, the portion other than the upper corner of the wall fitting portion 32k is denoted by 32n.

For the cam receiving member 32 of the present embodiment, a stress analysis simulation was performed for combinations of values of Δt and L similar to those shown in FIG.
The value of L, which is the threshold value for divergence between the value of Sc and the value of St, which change depending on the value of Δt, differs between the corner 32m and the other portion 32n at the upper end corner of the wall fitting portion 32k, A larger value was obtained at the corner of 32 m.

Results of the simulation are shown in FIG.
With Δt (=(W−t)/2) on the horizontal axis and L on the vertical axis, the result of plotting the value of L at which the value of Sc and the value of St begin to deviate is indicated by "▪". When the straight line obtained from "▪" is represented by an approximation formula, the following formula (4) is obtained.
L=0.5×Δt+0.9 Expression (4)

In the design of the cam receiving member 32, if the value of Δt is determined from the thickness t of the pressurizing lever member 31 made of a flat sheet metal member, the contact position 32a with the cam member 41 can be determined by the pressure of the cam receiving member 32. Cracks can be prevented from occurring by setting the side surface facing the wall portion 31k in the direction orthogonal to the thickness direction of the pressure lever member to a position larger than L obtained by Equation (4).
The “side surface facing” the wall portion 31k of the cam receiving member 31 means the side surface facing or contacting the wall portion 31k when the cam receiving member 31 is installed on the pressure lever member 31 .
That is, L2 is the dimension of the cam receiving member 32 in the direction orthogonal to the thickness direction of the pressing lever member 31, and the length from the contact position 32a with the cam member 41 to the side surface facing the wall portion 31k. When L2≧0.5×(W−t)/2+0.9, cracks can be prevented from occurring at the corner 32m.

Similarly, the variable Δt can be taken into account in equation (4), and the optimum shape can be determined by focusing only on the relationship between the contact positions 32 a between the cam receiving member 32 and the cam member 41 . After determining the optimum shape, the material of the cam receiving member 32 and the magnitude of the stress received from the cam member 41 should be considered. is eliminated, and an increase in cost can be prevented.

(Fifth embodiment)
An example of this embodiment is shown in FIGS. 27 and 28. FIG. The upper part of FIG. 28 is a schematic cross-sectional view of the fitting state of the cam receiving member 32 and the pressing lever member 31, and the lower part of FIG. be.
As shown in FIGS. 27 and 28A, the cam receiving member 32 includes a pressed surface 31a that receives the pressing force from the cam member 41 of the pressure lever member 31, and both sides of the pressure lever member 31 in the thickness direction. The bottom surface of the recess that is in contact with the surface to be pressed 31a extends to both sides in the horizontal direction. It is preferable to have

Similar to the example of the second embodiment described above, the cam receiving member 32 is a member having a substantially U-shaped cross section. In the cam receiving member 32 having such a shape, the corner portion of the area 32f (bottom surface of the concave portion) that contacts the pressure lever member 31 is subject to high stress and is easily damaged. If an R shape is provided to reduce the stress in that portion, the problem cannot be solved depending on the form of the shape, and other problems may occur.

FIG. 27(C) is an example in which both ends of the bottom surface of the recess are rounded. As a result of conducting a stress analysis simulation for the example of FIG. 27(C), it was found that the generated stress was reduced by about 30% compared to the unprocessed example.
However, in the example of FIG. 27(C), the corner of the contact surface of the pressure lever member 31 interferes with the R shape 32r of the cam receiving member 32. It becomes necessary to widen the width of the recess of the member 32 . Then, as shown in the examples of FIGS. 23A and 23B, there arises a problem that it becomes difficult to obtain the posture stability of the cam receiving member 32 and the pressing lever member 31 . In addition, high stress may be generated at both end portions 32q of the region 32f that abuts on the pressure lever member 31, and there is a risk that damage may easily occur.

On the other hand, FIG. 27(B) shows an example in which upwardly protruding rounded shapes are provided at both ends of the bottom surface of the recess. As a result of conducting a stress analysis simulation for the example of FIG. 27(B), it was found that the generated stress was reduced by about 30% compared to the unprocessed example, similar to (C).
However, in the example of FIG. 27(B), although the corners of the contact surface of the pressure lever member 31 do not interfere, the portion indicated by both ends 32q of the region 32f contacting the pressure lever member 31 is high. Stress may occur, which may make breakage more likely.

In FIG. 28(A), the bottom surface of the recess has a so-called relief-like groove 32r that extends to both sides in the horizontal direction and has semicircular R-shaped ends.
By forming the shape as shown in FIG. 28A, the side surface of the pressure lever member 31 and the contact surface of the cam receiving member 32 can be brought into contact with each other with an appropriate gap and width. Posture stabilizes.
As shown in the lower part of FIG. 28A, the bottom surface has flat portions 32p extending horizontally on both sides of a region 32f in contact with the pressure lever member 31, and is sufficiently wider than the width t of the pressure lever member 31. Since it is long, it is possible to prevent the occurrence of a portion where the stress is locally high.

As a result of conducting a stress analysis simulation for the example of FIG. 27(A), it was found that the generated stress was reduced by 84% compared to the unprocessed example. This is probably because the bottom surface of the concave portion has a long flat portion, which prevents concentration of stress and maintains a low stress state for the entire bottom surface. Therefore, in this embodiment, the cam receiving member 32 preferably has the shape shown in FIG. 27(A). In this way, by adopting a shape that can reduce the load stress at locations where breakage is likely to occur, early breakage of parts can be prevented, and durability can be improved.

(Sixth embodiment)
An example of this embodiment is shown in FIGS. 29 and 30. FIG.
29 is a perspective view showing an example of the shape of the contact surface of the cam receiving member 32 with the cam member 41. FIG. As shown in FIG. 29 , the surface of the cam receiving member 32 facing the cam member 41 has a substantially arc-shaped cross-section in the thickness direction (Y direction) of the pressure lever member 31 protruding toward the cam member 41 . is preferred.

29A and 29C show a shape in which the center of the surface facing the cam member 41 in the Y direction is convex in the direction of the cam member 41 . With such a shape, the length W in the Y direction of the surface (region) in contact with the cam member 41 is smaller than when the entire opposing surface is flat.
29(B) and 29(D), both ends in the Y direction of the surface facing the cam member 41 are rounded. 29(A) and 29(C), the length of the surface (region) in contact with the cam member 41 in the Y direction is reduced compared to the case where the opposing surface is flat. The height W becomes smaller.

In either case, as W decreases, Δt decreases, and the value of L obtained from the above equations (1) to (4) also decreases. That is, it is possible to prevent cracks from occurring in the cam receiving member 32 by setting L to be smaller.
However, there is a problem that the contact pressure increases while W becomes smaller (the contact area of the cam member 41 becomes smaller). Therefore, it may be necessary to consider the risk of early member destruction due to an increase in contact pressure and the influence of wear of the cam member 41 .

FIG. 30 is a Y-direction cross-sectional view showing a state in which the cam member 41, the cam receiving member 32, and the pressing lever member 31 are in contact with each other. 30(B) corresponds to FIG. 29(A), FIG. 30(C) corresponds to FIG. 29(B), FIG. 30(E) corresponds to FIG. 29(C), and FIG. corresponds to FIG. 29(B). For comparison, FIGS. 30A and 30D show an example in which the surface facing the cam member 41 is flat.
In any of the examples, the surface of the cam receiving member 32 facing the cam member 41 has a shape that protrudes toward the cam member 41, particularly a substantially arcuate shape, so that the surface (area) that contacts the cam member 41 is formed. The length W in the Y direction is reduced.

In the examples of FIGS. 30B and 30E, the cam receiving member 32 has a substantially arc shape protruding toward the cam member 41, and theoretically contacts the cam member 41 at one central point. However, since it is a member made of resin, the length W in the Y direction of the surface (region) in contact with the cam member 41 may change due to the effects of rigidity, wear, and the like. However, W is a sufficiently small value compared to the case of flat contact as shown in FIGS.

The fixing device of this embodiment can change the pressing force of the pressure roller by the above-described configuration. The pressure applied by the pressure roller is not limited to cases where it is changed according to the type of paper. It can also be applied in the case of reducing the pressure after passing the paper in order to suppress the plastic deformation of the paper. The present invention can also be applied to a fixing device in which the pressure roller is completely separated from the fixing roller (non-contact state) when the pressure is released.

Further, the fixing device to which the present invention can be applied is not limited to the fixing device provided with a pair of rollers (fixing roller and pressure roller) as shown in FIG.
For example, as shown in FIG. 31, the fixing device 12 may have an endless fixing belt 83 instead of the fixing roller. In the configuration shown in FIG. 31 , the heating means 22 and the nip forming member 81 are arranged on the inner peripheral side of the fixing belt 83 , and the pressure roller 19 is pressed against the fixing belt 83 at the position of the nip forming member 81 . Thus, a fixing nip 80 is formed.

Furthermore, the fixing device to which the present invention can be applied is not limited to the fixing device in which the pressure roller approaches and separates from the fixing roller as shown in FIG.
For example, as shown in FIG. 32, the fixing device 12 may be one in which the fixing roller 18 approaches and separates from the facing roller 82 facing the fixing roller 18 .
Further, the contact/separation mechanism according to the present invention can be applied not only to a fixing device but also to a transfer device that transfers an image onto a recording medium such as paper.

REFERENCE SIGNS LIST 12 fixing device 31 pressure lever member 32 cam receiving member 35 engaging structure 41 cam member 100 image forming apparatus

JP 2018-072792 A

Claims (10)

a pair of rollers that press against each other so as to freely contact and separate from each other, and nip and convey a recording medium;
a swingable plate-like pressure lever member having one end supported by a shaft and an elastic member engaged at the other end, and capable of pressing one of the pair of rollers against the other;
a cam member that displaces the pressure lever member between a position where the pressure contact state of the pair of rollers is maintained and a position where the pressure contact state is released;
a cam receiving member disposed at a position facing the cam member of the pressure lever member and transmitting a pressing force from the cam member to the pressure lever member;
Let t be the thickness of the pressure lever member,
W is the dimension of the cam receiving member in the thickness direction of the pressure lever member, and the length of the surface that contacts the cam member is W;
L1 is the dimension of the cam receiving member in the direction orthogonal to the thickness direction of the pressure lever member, and the length from the contact position with the cam member to one side surface is:
L1≧0.6×(W−t)/2+0.2
A fixing device that satisfies the following relationship: moreover,
L1≦1.3×(W−t)/2+1.25
2. The fixing device according to claim 1, which satisfies the relationship: The cam receiving member is
3. The apparatus according to claim 1, wherein at least one of the corners formed by the surface facing the cam member and the side surface of the pressure lever member in a direction perpendicular to the thickness direction thereof has an R shape. A fixing device as described. the cam receiving member is a member having a substantially U-shaped cross section,
3. The pressurizing lever member is fitted so as to cover at least a portion of both side surfaces in a thickness direction of the pressurizing lever member and a surface of the pressurizing lever member that receives a pressing force from the cam member. 4. The fixing device according to any one of 1 to 3. 5. The fixing device according to claim 1, wherein the cam receiving member and the pressing lever member have an engaging structure that engages with each other. The pressurizing lever member has a wall portion that protrudes in a direction perpendicular to the pressed surface that receives the pressing force from the cam member,
6. The fixing device according to claim 1, wherein the cam receiving member has a shape that fits into the wall. t is the thickness of the pressure lever member;
W is the dimension of the cam receiving member in the thickness direction of the pressure lever member, and the length of the surface that contacts the cam member is W;
L2 is the dimension of the cam receiving member in the direction orthogonal to the thickness direction of the pressure lever member, and the length from the contact position with the cam member to the side surface facing the wall portion is:
L2≧0.5×(W−t)/2+0.9
7. The fixing device according to claim 6, which satisfies the relationship: The cam receiving member is
a shape having a concave portion fitted so as to cover a surface of the pressing lever member to be pressed that receives the pressing force from the cam member and at least a part of both side surfaces in the thickness direction of the pressing lever member; 8. The fixing device according to any one of claims 1 to 7, wherein the bottom surface of the concave portion that abuts on the surface to be pressed extends to both sides in the horizontal direction and has an R-shaped groove portion at the end portion. 9. The surface of the cam receiving member facing the cam member has a cross section in the thickness direction of the pressure lever member that is substantially arcuate and protrudes toward the cam member. Any one of the fixing devices. An image forming apparatus comprising the fixing device according to any one of claims 1 to 9.

Images